Capacitors will restrict an instantaneous change in voltage. A capacitor, therefore, is useful to counter the destructive voltages generated at the switch contacts. When the contacts are closed, the capacitor is out of the circuit. As the contacts are opened any change in voltage is restricted by the capacitor if its value is large enough to restrict the voltage change to less than 1 V/ms.

A capacitor alone is not an ideal solution. When the contacts are open, the capacitor charges up to the supply voltage. As the contact is "made", an inrush of current results, limited only by a residual resistance, and damage may still result. For this reason, a resistor is configured in series with the capacitor. The higher the resistance value, the smaller the inrush current and the less effective is the capacitor. The voltage across the contacts when opened is equal to the load current x resistance (V = IR). It is recommended to keep V £ supply voltage. In this case, the maximum resistance of the network (R_N) will be equal to the load resistance (R_L).

The above formulas are recommended for determining the RC network parameters. They do not identify all of the subtleties but should serve as a guideline for effective results.